+1  A: 

Doh,

Dmitry, Application.Current doesn't have a property Width...

Use Grid instead of DockPanel:

<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"&gt;
   <Grid>
      <Menu Name="menu1" VerticalAlignment="Top">
         <MenuItem Header="File">
            <MenuItem Header="Open"/>
            <MenuItem Header="Close"/>
         </MenuItem>
      </Menu>
   </Grid>
</Page>

Don't overcomplicate things. And I really encourage you to read wonderful Dr. WPF articles: ItemsControl from A to Z

Cheers, Anvaka

Anvaka
Yes, my mistake, it should be:<Menu.Width> <Binding Path="MainWindow.Width" Source="{x:Static Application.Current}" UpdateSourceTrigger="PropertyChanged"/></Menu.Width>Thanks for reference.
Dmitry